Chemical and/or biological agent detection finds a wide variety of applications, such as detection of explosives and toxic chemicals in law enforcement and anti-terrorist efforts, environmental and agricultural contamination monitoring, medical diagnosis, and detection of chemical warfare agents.
The usefulness of carbon nanotube (CNT) structures in the field of chemical detection has been demonstrated. CNTs are molecular-scale ‘wires’. CNTs-based sensors are capable of detecting small concentrations of gas molecules. The conductance of CNTs can be substantially increased or decreased by exposure to certain gas molecules. Reference: Nanotube Molecular Wires as Chemical Sensors; Jing King, et al.; Science Magazine; Vol. 287; Jan. 28, 2000. Therefore, by measuring the change in an electrical property of a CNT sensors, such as resistance, capacitance, voltage or conductance, it is possible to detect the presence of a chemical that drives a change in that electrical property, and to identify the present chemical by comparing the magnitude, rate and direction of change of the electrical property to those changes known to result from exposure of the sensor to a particular chemical or biological agent.
CNT sensor technology is attractive because it may be implemented in a simple, compact, and relatively inexpensive apparatus. Further, CNT sensor technology is functional at ambient temperatures and provides rapid response times and reproducible responses.
There exist limitations and disadvantages associated with conventional methods and systems for application of CNT sensor technology to the detection of chemical and/or biological agents. These limitations fall generally into the categories of sensitivity, or the capability to detect a particular target agent, specificity, or the capability to specifically distinguish the agent that is detected, and false alerts.
A significant limitation in the utility and application of CNT sensor technology is limited sensitivity, or the ability of CNTs to detect certain agents or concentration levels of agents of interest. For example, carbon nanotube-based sensor systems do not have the capacity to detect low, yet dangerous concentrations of cyanogen chloride (CK), a key agent of interest in the field of chemical warfare detection.
In terms of specificity, a particular sensor may respond to a variety of chemical and/or biological agents. Adhering to the exemplar of CNT sensors applied to CK detection, there exist a plurality of chemicals that may alter the electrical properties of a CNT sensor, thereby providing an alert as to the presence of a chemical. Some of these chemicals may alter the electrical properties of the CNT sensor in the same direction, magnitude and/or rate as does CK. Therefore, it is possible to receive a false alert wherein the system may indicate the presence of CK when, in fact, CK is not present. Even a change in the relative humidity of the ambient environment in which a detection method is conducted may cause a change in the electrical properties of a CNT sensor.
What is needed is a system and method that may be implemented in a simple, compact, and relatively inexpensive apparatus that is functional at ambient temperatures, and provides rapid response times and reproducible responses. Further, the needed system and method must be capable of detecting chemical and/or biological agents of interest, differentiating the presence of the specific agent of interest from the presence of other present agents and, thereby, eliminating false alerts.